1. Field of the Invention
The present invention relates to semiconductor electronic components and to a method for fabricating such components and, more particularly, to an improved boron phosphorous silicate glass used as a layer on the semiconductor wafer which layer is substantially void-free for structures as narrow as 0.10 micron and with aspect ratios up to 6:1 and a method for forming the glass layer which includes a reflow temperature of about 750.degree. C. which temperature is lower than present and proposed fabrication requirements.
2. Description of Related Art
In the manufacture of semiconductor electronic components, it is necessary to encapsulate the component in a glass or to use a glass as an interlayer dielectric film. Typically, the glass layer is an SiO.sub.2 layer which is formed on the surface of the wafer using chemical vapor deposition (CVD). As the result of increasing demands of industry, the need for finer circuitry patterns and increased circuit density has made it necessary to develop improved glass layers for layering the semiconductor surfaces during the fabrication process. Of particular concern is the unevenness of the semiconductor substrate surface which becomes more critical as the circuit density and highly precise circuit patterns become finer.
In the early stages of forming glass layers on semiconductor wafers, an SiO.sub.2 layer was used as the glass material. These oxide glass layers were improved by the addition of dopants such as boron and/or phosphorous to the glass which dopants lowered the melting temperature and permitted the layers to be reheated to soften the glass and cause it to reflow to create a planar surface on the semiconductor device. As the circuit density and the need for fine circuit patterns have increased, however, it has been recognized that it is important to formulate and process oxide glass films to fill even smaller gaps on the surface of the semiconductor device without voids or bubbles within the oxide glass layer.
A borophosphosilicate glass (BPSG) is now used as an interlevel dielectric layer and has to provide a void-free fill of structures as narrow as 0.10 micron with aspect ratios up to 6:1. To fulfill this requirement, the BPSG layer is typically reflowed after deposition in the range of its glass transition temperature which is around 800-850.degree. C. The glass transition temperature is an important property of the glass and it is highly desirable that the reflow temperature be as low as possible for process effectiveness and to avoid temperature damaging effects to the semiconductor wafer during the fabrication process.
Boron and phosphorous doped silicon oxide layers (BPSG) are typically manufactured by reacting in a carrier gas and in the gaseous phase, tetraethylorthosilicate (TEOS), trimethylphosphate (TMP) or phosphine (PH.sub.3) and trimethylborate (TMB) or triethylborate (TEB) in the presence of oxygen and preferably with a small amount of ozone. The process can be carried out both in a plasma arc process, or at atmospheric pressure with ozone (at 350-600.degree. C.) or using a reduced pressure process at higher temperatures (e.g., 700-850.degree. C.). Typically, higher pressure processes use a low temperature process such as the deposition of BPSG by the co-oxidation of the reactants at temperatures of 400-600.degree. C. at a pressure of 50-760 torr (with ozone) and a temperature of 350-480.degree. C. at a pressure of 1-10 torr. Alternatively, a high temperature deposition process may be employed which uses low pressures such as about 0.5 to 5 torr and which process is performed in the temperature range of about 700-850.degree. C.
Broadly stated, it is highly desirable that the viscosity of the BPSG be low during the fabrication process to provide a void-free fill of structures as narrow as 0.10 micron with aspect ratios up to 6:1. The viscosity of the BPSG can be decreased by increasing the reflow temperature which is the temperature at which the deposited glass starts to flow and which is also commonly termed the glass transition temperature. The viscosity can also be decreased by increasing the dopant concentration of boron and phosphorous in the BPSG. In addition, the fill behavior of the glass is a function of the surface tension. F-doping increases the surface tension and decreases the viscosity both enhancing fill characteristics at lower temperatures.
The thermal budget for semiconductor devices, however, is limited to around 800.degree. C. for 30 minutes. Hence, an increase of reflow temperature is not desirable for many fabrication applications. Likewise, the dopant concentration is limited to around 5 weight percent each for B.sub.2 O.sub.3 and P.sub.2 O.sub.5 since exceeding this concentration results in surface crystal growth of boric acid or boric phosphate after deposition. Surface crystals are not desirable due to fabrication and integration problems with subsequent lithography, reactive ion etching (RIE) and chemical mechanical polishing (CMP) processes.
A number of patents have issued in this area to address improving BPSG films. U.S. Pat. Nos. 4,791,005; 4,845,054; 5,094,984; 5,104,482; 5,180,692; 5,286,681; and 5,354,387 show methods for making BPSG films on semiconductor substrates.
In European Publication No. 0562625, it is disclosed that oxygen atoms of the BPSG film may be replaced by non-bridging constituents such as atoms of halogen including fluorine. This breaks an oxygen bridge between the silicon atoms, and results in a lowering of the viscosity of the dielectric film. Exemplary is the replacement of part of the oxygen in a BPSG film with fluorine to lower the dielectric film flow temperature to about 850.degree. C.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an improved method for forming a borophosphosilicate glass on a substrate such as a semiconductor wafer which glass has improved gap-fill properties and a low reflow temperature.
It is another object of the present invention to provide a substrate such as a semiconductor wafer having a layer of a borophosphosilicate glass thereon which glass has improved gap-fill properties and a low reflow temperature.
A further object of the invention is to provide a borophosphosilicate glass with enhanced gap fill capability to provide a void-free fill of structures as narrow as 0.10 micron with aspect ratios of 6:1.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.